In his article “Metaphysics in Aristotle’s Embryology” (Proceedings of the Cambridge Philological Society 214 [1988]), John Cooper argues that it is wrong tothink that the movements that come from the female in Aristotle’s version of animal generation play any sort of formal role in the resultant offspring. In this paper I raise some doubts about Cooper’s thesis through a consideration of three key passages from the Generation of Animals (GA IV.1 766b15–16, IV.3 767b22–23, and IV.3 768a12–14) which open a discussion of Aristotle’s views on the distinctions between form and matter, active and passive principles, deficiency, summetria, and, more generally, the importance of being sensitive to the analogous uses of terms